A number of traditional ways exist for forming images on a printing plate. These include, but are not limited to, molding, photoflash imaging, and thermal imaging. The present invention is directed broadly to the area of thermal imaging or thermography. Thermal imaging or thermography is a process wherein an image is generated by the use of image-wise modulated thermal energy. Traditionally, "direct thermography" refers to a method whereby a visible image pattern is formed by the image-wise heating of a recording material containing matter that by chemical or physical process changes color or optical density. Most of the direct thermographic recording materials are of a chemical type. Upon heating the recording material to a certain conversion temperature, an irreversible chemical reaction takes place and a colored image is produced.
In recent years, the field of manufacturing or producing printing plates (e.g., rubber stamps) has experienced rapid advancement. Resinous relief printing plates, planographic printing plates, and intaglio printing plates all formed using photosensitive resins now enjoy widespread use. In addition, a number of methods are known for forming printing plates using stencil images. These methods generally involve the use of a thermal printer or a wire dot printer to form a stencil image on a sheet, which is then utilized as a printing plate.
As the use of relatively simple printing systems has expanded, the need for a simple, yet reliable, method of printing a printing plate has come into existence. In an attempt to address this need, U.S. Pat. No. 5,665,524 (which is hereby incorporated herein in its entirety by reference) describes a printing plate which is formed from an open celled thermoplastic medium wherein the open cells are sealed upon exposure to energy rays. The methods described in this reference generally require the presence of a negative to block photorays which results in a portion of the photosensitive thermoplastic medium remaining unhardened by the blocking of the energy rays, and a separate portion which is hardened by exposure to the energy rays. The exposed portion forms a background of the image to be formed on the stamp. The background portion prevents the transfer of ink from the thermoplastic foam to the receiving medium (i.e., paper) in these regions. It is speculated in U.S. Pat. No. 5,665,524 that an expensive laser system may be driven to seal predetermined portions of the foam to form the background image. This reference also places a great deal of emphasis on forming the open-cell image in the same plane as the background image by sealing only a surface layer of open cells, thereby forming a plate having little or no relief.